Advances in polymerization and catalysts have produced new polymers having improved physical and mechanical properties useful in a wide variety of products and applications. With the development of new catalysts, the choice of polymerization, such as solution, slurry, high pressure or gas phase, for producing a particular polymer has been greatly expanded. Advances in polymerization technology have also provided more efficient, highly productive and economically enhanced processes.
With these advances, a number of different techniques have been developed for delivering catalysts to polymerization reactors. One technique involves delivery of the catalyst to the reactor in a slurry with the catalyst suspended in a hydrocarbon liquid. Another technique involves use of an olefin monomer (e.g., ethylene) as a carrier gas for catalyst delivery. While olefin monomers have been used successfully for catalyst delivery, their use is challenging for catalysts, such as chromium-based catalysts, in which the catalysts are reduced and activated by the monomer without a co-catalyst. As such, the carrier gas for delivering such catalysts typically cannot be an olefin monomer, as this would likely cause polymerization and plugging in the catalyst delivery system. Because it is non-reactive with the catalysts, nitrogen has been used as an alternative carrier gas for catalyst delivery. However, to prevent nitrogen accumulation in the reactor, a reactor vent may be required. This is especially problematic in reactors without a vent recovery system, leading to undesirable loss of monomer. In general, a vent recovery system is any system used to recover selected components from the reactor vent. Even further, loss of monomer through the reactor vent may be exacerbated in reactors operating at high ethylene partial pressures.
Accordingly, there exists a need for improved methods of catalyst delivery, for example, to reduce the amount of nitrogen feed to the polymerization reactors and, thus, reduce the reactor vent to remove nitrogen.